1. Field of the Invention
The present invention relates generally to circuit guarding and particularly to circuit guarding to protect circuits associated with integrated circuits operational amplifiers from internal (self-generated) leakage currents.
Techniques for shielding or guarding circuits or networks from the effects of leakage currents are well known. In general there are two types of guarding circuits used to prevent or inhibit leakage currents. One type, known as passive guarding, utilizes one or more conductors positioned adjacent to the active or signal circuits of concern and grounded to a common bus to serve as a shield, receptor, or sink of stray currents due to leakage effects. The other type is an active guard circuit which utilize conductors suitably placed adjacent to the active or signal circuits of concern, but provided with voltage potentials derived from the circuit of concern itself and arranged to divert leakage currents in such a manner as to minimize the effect of such currents on the circuit of concern. For a discussion of several design techniques, see an article entitled "New Design Techniques for FET Op Amps" published in the National Semiconductor Application Note (pages 5 and 6) AN-63 (March 1972).
Nevertheless, in certain applications, such as in air pollution control, medical electronics, space, instrumentation devices of high sensitivity and, in general, any application in which a high impedance circuit may be subject to deleterious effects of leakage current are still of concern, there is a need for a guard circuit that will minimize if not inhibit leakage currents, particularly, in the environment of printed circuit boards, hybrid circuit substrates, and integrated circuits.